The CDC discovered the man's cancer cells contained tapeworm DNA.

As if a tapeworm infection wasn’t bad enough, researchers have identified a bizarre and fatal case where a man sprouted cancerous tumors generated by the parasite.

In a case that rattled researchers at the Centers for Disease Control, a Colombia man died after a tapeworm he was carrying developed cancer cells and transmitted them to its human host.

It’s the first such case ever identified, according to a review of the case published today by the New England Journal of Medicine.

“This is the first time we've seen parasite-derived cancer cells spreading within an individual," CDC researcher Dr. Atis Muehlenbachs told the Washington Post. "This is a very unusual, very unique illness."

The case came to light after the 41-year-old man reported to a clinic in Medellin complaining of fever, weight loss and weakness. Doctors found tumors in his neck, lungs and liver – but were astounded to learn that the tumors contained unidentifiable non-human cells.

Baffled, the doctors called in the CDC, which after tests linked the cells to the DNA of the common dwarf tapeworm, to researchers’ shock.

“Discovering these cells had tapeworm DNA was a big surprise — a really big surprise," Muehlenbachs told the Post.

The man was also HIV-positive, and scientists believe tapeworms – most likely spawned from eggs ingested in contaminated food – were allowed to wreak havoc due to his compromised immune system. He died within several days after researchers figured out the source of his tumors.

Scientists previously hadn’t believed that such a thing was possible.

"We didn’t believe that cells from a human parasite could become malignant and then invade human tissue," Bobbi Pritt, director of clinical parasitology at the Mayo Clinic, told the paper.

Now that they’re aware it can happen, they theorize that there may be similar such cases that have gone unrecognized. The dwarf tapeworm is the world’s most common, infecting up to 75 million people at any given time.